Core for molds for electrically melting metals for casting hollow ingots

ABSTRACT

Mold core for electrically melting metals for casting hollow ingots wherein the core wall is divided lengthwise on its periphery and is designed to be taken apart. The wall is preferably made of at least two partial cylinders between which stave-like keys are positioned which can be removed inwardly.

BACKGROUND

This invention relates to a core for molds for the electrical melting ofmetals to form hollow ingots, especially for the slag-shieldedelectrical melting of consumable electrodes, having a wall whose outsidedimensions correspond to those of the hollow of the ingot.

The production of hollow ingots, especially by the slag-shieldedelectrical melting of consumable electrodes, has long been known. Incontrast to the method of producing a solid cast ingot and thenperforating it, hollow ingot casting has the advantage of a virtuallycomplete utilization of the material and the formation of ahigh-quality, fine-grain structure substantially free of voids andsegregations. The reason for this lies in the short distance betweenevery element of the volume of the hollow ingot and the cooled moldwalls, i.e., in a favorable ratio of the internal and external surfacearea of the hollow ingot to the volume thereof. For the manufacture ofhollow bodies such as tanks, hoops or tubes it would therefore bedesirable to cast them directly as hollow bodies.

To produce a hollow ingot, it is necessary to provide within the mold acore which during the production of the ingot is withdrawn from theingot or from the portion thereof which has solidified. A very seriousproblem is the unavoidable shrinkage of the ingot during cooling, whichentails the danger that the ingot may shrink tight on the core.

In casting processes modeled on continuous strand casting, in which amold with a core fastened therein moves relative to the hollow ingot,there is the danger that the core might "freeze" in the ingot, bringingthe entire casting process to a halt and necessitation shut-down. Incasting processes using a stationary mold and stationary core, there isthe danger that the ingot may shrink tight on the core such that it canno longer be released undestructively from the ingot.

To obviate the problems described above, it has long been known to makethe core of foundry sand, and after solidification and cooling of theingot, to remove the core by destroying it. Such a sand core, however,has the disadvantage of poor thermal conductivity and therefore of anunfavorable influence on grain structure. Especially, however, it is notsufficiently resistant to a superheated molten metal, and particularlyto molten slag, which has the tendency to dissolve ceramic compositionsand hence also foundry sand. Inclusions of particles of foundry sand inthe hollow ingot are especially dangerous.

It is consequently necessary to use metal cores, which must necessarilybe liquid cooled. In order in this case to prevent the hollow ingot fromshrinking tight on the core, attempts have already been made to make thewall of the core a corrugated wall having corrugations running parallelto the long axis of the core, so as to provide it to some extent with anelastic compressibility. In this case, however, a correspondingcorrugated profile is necessarily formed on the inside of the hollowingot, and has to be removed by a difficult working procedure.Furthermore, the ingot fills the grooves between the corrugations of thecore, so that the radial compressibility is largely lost. Such attempts,therefore, have not resulted in success.

Attempts have furthermore been made to make only the surface of a metal,water-cooled core compressible radially. For this purpose it has becomeknown to coat the core surface with a compressible, inorganic layer ofmaterial of good thermal conductivity, although the selection of thematerial has been left open. Thus far no material has become known whicheven remotely corresponds to these requirements. It must be consideredthat the nature of such a substance excludes good thermal conductivity.Furthermore, as already stated above, virtually all ceramic materialsare attacked by hot, molten slag, so that a core coated in this mannerwould not last through a single casting operation.

SUMMARY

The invention is therefore addressed to the problem of devising a coreof the kind described above, whose outer surface corresponds to theshape of the ingot cavity, and which can be removed from the ingot evenafter the ingot has shrunk tight on the core.

The solution of this problem is achieved in accordance with theinvention in the core described above in that the core wall is dividedlengthwise on its periphery and is designed to be taken apart. It isespecially desirable that the wall be composed of at least two partialcylinders between which stave-like keys are disposed, which areremovable inwardly.

Such a core wall is assembled from its constituent parts prior to thecasting of a hollow ingot by electrical melting, making use ofappropriate clamping and spreading means, and it is disposed in agenerally concentric manner within a mold. After the hollow ingot hasbeen formed between the core and the mold, the ingot shrinks fast ontothe core. By simple disassembly, however, especially by the inwardextraction of the stave-like keys, the core can be removed piece bypiece from the ingot cavity and re-used for the next casting operation.

It is especially desirable for the contact surfaces between the partialcylinders and the keys to be at an acute angle to a radial plane whichis the plane of symmetry of the keys, the base of the angle beingdirected outwardly. If the pressure of the ingot on the core shouldbecome excessively great, and if the aperture angle of the contactsurfaces between the partial cylinders and the plugs is appropriatelyselected, the keys will be forced slightly inwardly, permitting thepartial cylinders to move toward one another to a corresponding extent.The end result will be a reduction of the diameter of the core which canthus yield to the great compressive stresses of the hollow ingot.

DESCRIPTION OF THE DRAWING

Additional advantageous developments of the subject matter of theinvention are given in the following description taken in conjunctionwith the accompanying drawing wherein

FIG. 1 is a vertical cross-sectional view taken through the mold part ofa slag-shielded electrical melting apparatus for the production of ahollow ingot,

FIG. 2 is an enlarged horizontal cross-sectional view taken along lineII--II of FIG. 1,

FIG. 3 is also an enlarged horizontal cross-sectional view taken alongline III--III of FIG. 1, and

FIG. 4 is a detail view taken within the circle D (IV) of FIG. 1.

DESCRIPTION

In FIG. 1, a mold 11 is placed on a mold bottom 10 and is surrounded bya cooling jacket 12. Underneath the mold bottom 10 there is a coolingwater case 13 having an inlet 14 and an outlet 15.

A core 16 in inserted into the mold bottom 10 and consists of twopartial cylinders 17 and 18 and of two stave-like keys 19 and 20 ofwhich only the back one 20 is shown in phantom in FIG. 1. Additionaldetails can be seen in FIGS. 2 to 4. The bottom end 21 of the coreextends considerably into the water case 13, thereby increasing thecooling surface considerably. The partial cylinders 17 and 18 areprovided on their outer periphery with flange sectors 22 and 23 whichare bolted sealingly but releasably to the mold bottom 10. The boltingand sealing of the flange sectors must also permit a radial displacementof the partial cylinders 17 and 18. This also is true of a top closureplate 24 in whose center an additional cooling water outlet 25 isdisposed. With this cooling water outlet it is possible to produce anupward flow of cooling water through the core 16 from the water case 13.The cooling system provides protection also for the necessary seals.

Between the mold 11 and the core 16 there is formed a cylindrical cavity26 in which a hollow ingot 27 has begun to form, at the top of whichthere is a pool of molten metal 28. On this pool of molten metal floatsa molten layer of slag 29 in which a plurality of consumable electrodes30 are immersed at equal intervals about the circumference of the mold.Between these electrodes and the hollow ingot 27, or between adjacentelectrodes, there is a difference of potential on the basis of which aflow of electric current is produced through the slag layer 29,resulting in the melting of the electrodes. Details of this process,however, are in the state of the art, so that further explanations canbe dispensed with.

In FIGS. 2 and 3, the core 16 has a cylindrical external surface 31corresponding to the cavity in the ingot and formed by the envelopesurface of a cylinder 32 formed by the partial cylinders 17 and 18 andby the stave-like keys 19 and 20. Between the partial cylinders 17 and18 and the keys 19 and 20 are the interfaces 33 and 34 disposed at anacute angle to a radial plane E--E which is the plane of symmetry of thekeys 19 and 20. The base of this angle is directed outwardly, the angleopening such that the keys 19 and 20 can slip inwardly.

Between the keys 19 and 20 a plurality of spreader jacks 35 isdistributed through the height of the core, these jacks having aresilient member, not shown in detail, which permits the keys 19 and 20to yield toward one another to a limited extent. In the present case thespreader jacks 35 are screw jacks composed of a threaded sleeve 36 and athreaded spindle 37, each mounted in one of the keys. By turning thethreaded sleeve 37 it is possible to force the keys 19 and 20 apartagainst the partial cylinders 17 and 18. A seal is provided by thegaskets 38.

As shown in FIG. 3, draw jacks 39 are disposed between the partialcylinders 17 and 18, and they, too, are distributed through the heightof the core between the spreader jacks 35 and at right angles thereto.The draw jacks 39 consist each of two oppositely threaded spindles 40and one spindle nut 41. The outer ends of spindles 40 are hooked intothe eyes 42 and 43 which are affixed to the partial cylinders 17 and 18.In this manner the partial cylinders 17 and 18 can be drawn against thekeys 19 and 20.

It can be seen in FIGS. 2 and 3 that the keys 19 and 20 are of asomewhat T-shaped cross section, and that the crossbar of the T bearsagainst the partial cylinders from the inside, the gaskets 38 beingdisposed between the crossbar and the partial cylinders on both sides ofthe stem of the T.

FIG. 4 shows how the unavoidable seam between the flange sectors 22 and23 is sealed. For this purpose, the ends of the flange sectors 22 and 23are provided with slanting surfaces 44 and 45 forming a V-shaped gap. Asealing body 46 of matching shape is placed in this gap and forms aprolongation of a flange plate 47 which is tightened against the flangesectors 22 and 23 by means of two bolts 48. When all of the bolts havebeen removed and the sealing body 46 has been removed, the flangesectors 22 and 23 can be driven inwardly against one another so that theingot can be separated from the core 16.

What is claimed is:
 1. A mold core for the electrical melting of metalsto form hollow ingots, comprising: means forming a longitudinallydivided and disassemblable cylindrical wall having outer dimensionscorresponding to that of the ingot cavity, the means including at leasttwo partial cylindrical shells and at least two inwardly removablestave-like pressure members each having a radial portion extendingbetween two shells, and abutting same along two contact surfaces, acrossbar bearing from within on the cylinder shells to define with theradial portion a generally T-shaped cross section for each pressuremember and gasket means between the crossbar and the inner surface ofthe shells for providing a liquid-tight seal, thrust tightening meansconnected between the pressure members for radially moving same anddraft tightening means connected between the shells for radially movingsame.
 2. The core of claim 1, wherein the contact surfaces between theshells and the radial portion of the pressure members are at an acuteangle with respect to the radial plane extending symetrically throughthe pressure member the vertex of the angle directed outwardly.
 3. Thecore of claim 1 further comprising a bottom wall through which thebottom ends of the cylindrical wall extends and a water enclosurepositioned below the bottom wall and into which the cylindrical wallextends and means coactive with the cylindrical wall for sealing thebottom wall with respect to the water enclosure.